This is a revised request for a Senior Scientist Award (K05) to support my programmatic research into the development and regulation of sleep and circadian rhythms in children and adolescents. The research plan focuses on 3 projects in my laboratory. The projects are driven by my conceptual model of processes that influence the developmental trajectory of sleep/wake and related behaviors. The model includes 4 processes: maturation, behavior(including psychosocial aspects), homeostasis, and circadian rhythms. "Sleep Patterns and Waking Vulnerabilities in Adolescents" uses a combination of field and in-lab measures to examine adjustment to early school start time. A second study focuses on sleep patterns and daytime sleepiness in high school students who have jobs or are involved in organized athletics. Results of these studies may have practical implications for school starting times and may inform us about the optimal times for students to be working at jobs or practicing for sports. "Circadian Rhythms, Sleep, and Depression Risk at Puberty" includes a series of studies with a much more basic focus. Laboratory measures of circadian phase, amplitude, and period are taken in normal children using challenging research protocols, such as the Constant Routine and Forced Desynchrony. The research focuses on identifying whether and to what extent puberty directly affects parameters of the circadian timing system in humans. A further aspect of this project examines the circadian timing system across puberty in adolescents at risk to develop depression by virtue of family history. "Developmental Manifestations of Daytime Sleepiness" uses sleep restriction paradigms to challenge children (ages 6 to 15 years) either acutely (one night), chronically (two weeks), or repeatedly (one week on two occasions). Outcome variables are in 4 domains: physiological sleepiness; behavioral manifestations (impulse control, activity level); performance variables; and introspected sleepiness. These studies examine whether response to sleep restriction manifests differently in younger versus older children in the behavioral and performance domains and whether puberty independently affects the responses. I plan to teach undergraduates at Brown University, to continue my Undergraduate Sleep Research Apprenticeship program, and to teach younger students as I work with schools. I will continue to mentor postdoctoral fellows and young faculty. Professional enhancement will come in areas of computerized EEG analysis, development of field measures, enhanced expertise in circadian rhythms research and analytic methods, new methods for assisting emotion expression and regulation, and development of an animal model for my adolescent circadian rhythms project.